The present invention relates to a medical anesthetic needle including a hollow outer needle having the front end thereof slightly bent upward from the needle axis when the needle axis is laid horizontal, and a solid inner needle being inserted into and through the outer needle from the rear thereof movably inward and outward.
In operating an anesthetic needle having the axis of the front end thereof inclined upward from the needle axis, a human body is punctured or penetrated into with the anesthetic needle under the condition that a solid inner needle is inserted into and through a hollow outer needle thereof. Then, after the inner needle is drawn out, an instrument, such as a catheter for injecting anesthetic, is inserted instead. The reason for inserting the inner needle into and through the outer needle when the human body is penetrated into with the anesthetic needle, is to reinforce the outer needle, and, at the same time, to prevent human tissue from entering inside the outer needle.
The blade surfaces of the outer and inner needles intersect the axes of their respective front end portions at their respective predetermined blade surface angles. The blade surface of the inner needle is of a solid elliptic shape, and is fitted into the blade surface of a hollow elliptic shape located at the front end of the outer needle, approximately flush with the blade surface of the outer needle, to seal the opening of the blade surface of the hollow outer needle. In case, however, an entire front end portion of the inner needle was formed in the same shape and size as the hollow region of the front end portion of the outer needle having the front end thereof bent, then, the front end portion of the inner needle was not possible to insert into and through the outer needle from the rear end thereof. Thus, the front end portion of the inner needle used to be partially cut off so that the front end portion, as bent, of the inner needle is easily deformed elastically, thereby enabling the front end portion of the inner needle to insert into and through the outer needle from the rear end thereof.
Conventional inner needles used to be worked using a method shown in FIG. 6. The working method included a first step of bending the front end portion of a piece of stainless steel wire W having a diameter D approximately equal to the inner diameter of an outer needle, upward at a predetermined angle xcex8, relative to the horizontal, as shown in FIG. 6(a); a second step of cutting the piece of stainless steel wire W at a slant plane that passes through a point A located on the top surface line of a portion of the piece of stainless steel wire W bent upward, and higher than the top surface line of a portion of the piece of stainless steel wire W left straight and laid horizontal, by a predetermined distance h, and that intersects the axis of the portion of the piece of stainless steel wire W bent upward, at a predetermined angle xcex8, relative to the horizontal, to form a blade surface of the inner needle of a solid elliptic shape; and cutting the piece of stainless steel wire W to have the inner needle having an entire length equal to a predetermined length L, as shown in FIG. 6(b); and a third step of cutting off a portion of the piece of stainless steel wire, by means of machine cutting, that is located below a horizontal plane M passing through a position located at a height from the bottom surface of the piece of metallic wire greater than the radius of the piece of stainless steel wire, in a region located forward of a vertical plane passing through a position B located to the rear from the point A by a distance not less than three times the diameter D of the piece of stainless steel wire, when the piece of stainless steel wire has the axis thereof laid horizontal with the blade surface (5) placed facing upward, to form the inner needle 30, as shown in FIG. 6(c).
The first step of bending the piece of metallic wire W of a circular cross section, however, had a problem of generating many off-specification products, resulting in increased manufacturing cost, because of an extensive amount of springback being caused, thereby increasing dispersion in the inclination angle xcex8.
The present invention is made to solve the problem described above. Thus, an object of the present invention is to provide a solid inner needle that is capable of being inserted into and through an outer needle of a medical anesthetic needle having the front end thereof slightly bent, from the rear end of the outer needle movably inward and outward, and that has a shape enabling a great reduction in the manufacturing cost thereof.
An inner needle, according to the present invention, comprises: a blade tip portion having a blade surface that plugs the opening of a blade surface of a hollow outer needle having the front end thereof bent upward; a columnar portion having a diameter approximately equal to the inner diameter of the outer needle; and a connecting portion connecting the blade tip portion and the columnar portion together in one piece. The connecting portion is of a split-columnar shape, having the circular circumferential surface thereof extended flush to the circumferential surfaces of the blade tip portion and the columnar portion, having an axial length not less than three times the diameter of the columnar portion. The connecting portion has the bottom surface thereof positioned higher than the axis of the columnar portion, and is bent so that the upper end of the blade surface is located higher than the top surface line of the columnar portion by a predetermined distance and that the axis of the blade tip portion is inclined at a predetermined angle relative to the horizontal, when the inner needle has the axis thereof laid horizontal with the blade surface placed facing upward.
The inner needle described above, is manufactured using a method, when a piece of solid metallic wire having a diameter approximately equal to the inner diameter of the hollow outer needle, has the axis thereof laid horizontal, comprising: a first step of cutting the front end of the piece of metallic wire at a plane inclined at the same angle as the blade surface angle of the inner needle to form a blade surface of an elliptic shape; a second step of cutting off a portion of the piece of metallic wire that is located below a horizontal plane positioned at a height from the bottom surface of the piece of metallic wire greater than the radius of the piece of metallic wire, in a region located between the upper end of the blade surface and a position distant to the rear from the upper end of the blade surface by a distance not less than three times the diameter of the piece of metallic wire, to form a blade tip portion including the blade surface, and a connecting portion of a split-columnar shape; and a third step of bending the connecting portion so that the upper end of the elliptic-shaped blade surface is located higher than the horizontal top surface line of the columnar portion by a predetermined distance, and that the blade tip portion has the axis thereof inclined upward at a predetermined angle; and cutting the piece of metallic wire to have an entire length equal to a predetermined length.
The blade surface angle of the inner needle is preferably set to be equal to or slightly greater than the blade surface angle of the outer needle so that, when the elliptic-shaped solid blade surface of the inner needle is fitted into the elliptic-shaped hollow blade surface of the outer needle with the centers thereof aligned, the lower portion of the blade surface of the inner needle is prevented from protruding from the blade surface of the outer needle, thereby reducing pain caused by puncture.
The vertical width of the connecting portion of the inner needle is preferably made not more than 0.4 times the diameter of the columnar portion to improve precision in the bending work. When, for example, making the vertical width of the connecting portion approximately 0.2 times the diameter of the piece of metallic wire, the connecting portion becomes flat, which not only makes the bending work easy but also improves precision in the bending work, resulting in a very low ratio of off-specification product occurrence.
As described above, the inner needle of the present invention is bent upward in accordance with the front end portion of the outer needle, where the portion to be bent is not a columnar body having a circular cross section of prior art, but a flat split-columnar body having the vertical width or height smaller than the bottom side width thereof, and besides the bottom side width is smaller than the diameter of the circular cross section of prior art, thereby causing the amount of springback in the bending work to be very small compared with the cases of prior art. As a result, precision in the bending work is remarkably enhanced, the yield improves, and the manufacturing cost is sharply reduced.
The front end region of an inner needle manufactured in the way as described above, with the axis thereof laid horizontal and the blade surface thereof placed upward, comprises a blade tip portion having the blade surface, and a connecting portion extending from the rear end of the blade tip portion, having a split-columnar shape with a cross section of an area smaller than that of a semicircle, where the rear end of the connecting portion is connected to the columnar portion of the inner needle together in one piece. The circular circumferential surface of the connecting portion is extended flush to the circumferential surfaces of the blade tip portion and the columnar portion. The bottom surface of the connecting portion is at a position higher than the axis of the columnar portion. When inserting the inner needle into the outer needle from the rear of the outer needle, the blade tip portion having a diameter approximately equal to the inner diameter of the outer needle enters first, and the flat connecting portion follows. At this time, since the connecting portion deforms elastically, the columnar portion having a diameter approximately equal to the inner diameter of the outer needle that follows thereafter, is capable of being smoothly inserted into the outer needle.
When the blade tip portion is formed so that the rear end surface has the lower end thereof positioned axially forward relative to the upper end of the front end surface of the blade tip portion, thereby decreasing the axial length of the circumferential surface of the blade tip portion, then, the front end region of the inner needle is enabled to move through the hollow region of the outer needle further smoothly.